Field of the Invention
The present invention relates to a sound processing device and a sound processing method.
Description of Related Art
It is known that a speech recognition rate is lowered when speech is recognized in a noisy environment. It has been proposed that the lowering of a speech recognition rate is suppressed by suppressing background noise included in an input sound signal has been proposed.
Since suppression of background noise causes distortion in a component of speech uttered by a person, a speech recognition rate may not be satisfactorily raised or the speech recognition rate may rather be lowered. In this regard, for example, Japanese Patent No. 5041934 (Patent Document 1) discloses a process of adding white noise to a sound signal whose noise has been suppressed to reduce an influence of distortion. In the process disclosed in Patent Document 1, the influence of distortion due to suppression of noise may be alleviated to raise the speech recognition rate by increasing an addition amount of white noise.
However, since the addition of white noise relatively decreases a speech component, the speech recognition rate may be lowered.
On the other hand, for example, Japanese Unexamined Patent Application, First Publication No. 2010-271411 (Patent Document 2) discloses a noise suppression device that includes first noise suppression means for extracting noise components from sound signals of multiple channels, estimating stationary noise included in the noise components, and subtracting a spectrum of the stationary noise from spectrums of the sound signals of the channels based on a subtraction coefficient. The noise suppression device estimates a spectrum of non-stationary noise by subtracting the spectrum of stationary noise from the spectrums of the noise components of the channels and generates a filter coefficient for emphasizing a target sound component from the spectrum of non-stationary noise. The noise suppression device also includes second noise suppression means for performing a filtering process using the filter coefficient on the sound signals of multiple channels having been processed by the first noise suppression means. The noise suppression device calculates a kurtosis variation index indicating a degree by which a kurtosis in a frequency distribution of intensity of the sound signals varies before being processed by the first noise suppression means and after being processed by the second noise suppression means and variably controls a subtraction coefficient based on the calculated kurtosis variation index.
However, the noise suppression device disclosed in Patent Document 2 determines a spectrum subtraction coefficient based on the kurtosis variation index as an index of a directivity difference between a target sound and noise and suppresses the background noise included in the sound signals of multiple channels, and thus the processing load thereof is excessively large. Therefore, the speech recognition rate could not be enhanced through the use of a process with a relatively small load, such as the process of adding auxiliary noise such as white noise in the sound processing device disclosed in Japanese Patent No. 5041934.